Support: 16/Oct/2007, Rachel Gaulton/Tim Malthus, GB06/05

Description

Rachel contacted us with a problem relating to radiometric calibration.

I'm not sure who specifically is the best person to ask about this,
but I am having some problems with the AISA Eagle data recently
delivered for my sites (Clocaenog and Glasfynydd, acquired July 06).
The radiance values differ considerably to those of the CASI and ATM
data acquired at the same time, specifically they are much lower
(about 1/2 to 2/3) in the Eagle data (see attached spectra of a paved
area in Glasfynydd for an example). Following attempts at atmospheric
correction, this results in significantly lower reflectance than is
expected based on ground spectra. I may be missing something obvious
(e.g. different units), or is this down to errors in the radiometric
calibration of the Eagle sensor?

Chris from FSF is visiting in early Dec to calibrate some instruments for 2008. While there, get him to do a quick and dirty calibration on the Specim too, so we have a calibration made in the same conditions as the CASI one to compare against (giving us a ground truth). This will establish if there's a problem with Specim's calibration procedure.

As soon as Bill is back from holiday (~10th Nov?), ask him to check on how he handles the Specim calibration in azspec, particularly with non 1-1 binnings (all 2007 Eagle flights are 2-1 or higher and the calibration is 1-1).

#81 shows tentative hints it may be related to spatial binning - Rachel's flight is 195c/2006, which was 2 spectral, 2 spatial. Going to contact Rachel so she knows we're working on this and have some initial results.

re. the Eagle radiometric calibration issues (or software bug), I've
been keeping an eye on your internal tracking of the issue and your
clearly making great progress with it! However, I was just wondering
if there was any chance you would be able to give me some sort of
indication (even very approximate) of when you think it is likely that
you will manage to resolve the issue and over what approximate
time-scale, if at all, I could expect to receive corrected data? I
appreciate you may well not be able to answer this, I just thought it
was worth asking as I am now in the 4th year of my PhD and really need
to be able to produce a final plan of my thesis and re-think sections
if necessary (the Eagle/Hawk data would have comprised the basis for
at least a chapter).
Thanks for any help - best guesses are fine!

Explained the current situation - likely timeframe would be several months, even if the fix was immediately available now.

We've offered to try processing her data via the Caligeo route, if she can help us verify it's workable.

Rachel agreed to try this - selected flightline is 195a, eagle, line 6? ("e195061b"). Contacting AKW to see if he has the previous script / parameters.

Many thanks for your reply, I appreciate its hard to predict how long
this will take, I was just keen to get some idea. If you are willing,
I would be very grateful if you could try processing a strip with
Caligeo - the most suitable would be one of the Glasfynydd strips -
e195061b as this has some areas I have field spectra for. Don't worry
if it takes a few weeks until you can do this - I am still writing up
my lidar work anyway so have plenty to keep me going.
If this works it may not be necessary to process all of the remaining
data immediately, my research plots cover a relatively small area so a
smaller number of flight lines would be sufficient (for the time being
at least).

Rachel confirmed that the AISA tools output was of acceptable quality so I'm processing the remainder of her eagle flight lines. I'm using Bill's new azspec version to do it with rather than AISA tools because that's faster and appears to give the same output on checking.

I have sent the Glasfynyyd data to Rachel via FTP (and told her the above and suggested she have a quick check that it's what she's expecting) and am currently processing the Clocaenog data.

Clocaenog data delivered to Rachel. However, the Eagle data for Clocaenog do not line up with each other or with the previously-processed ATM and CASI - boresight numbers are believed to be slightly wrong (previous flight lines using these boresight numbers showed what is appeared to be slight inaccuracy with the pitch offset). Inaccuracy relative to ATM and CASI is quite large though, plus the CASI image seems to be stretched across the line of flight compared to the Eagle data, so it may be there is some other source of inaccuracy as well.

Rachel says that she needs the flight lines to align correctly if at all possible (not necessarily exactly in the correct position geographically, but aligned relative to each other), so need to get vectors for the area to check correct positioning.